The present invention relates to a remote emissions sensing system and method for sensing exhaust emissions from motor vehicles where the system determines the opacity of an exhaust plume.
Remote emission sensing (RES) systems are known. One such system is disclosed in U.S. Pat. No. 5,210,702 and comprises an electromagnetic (EM) radiation source that is arranged to pass a beam of EM radiation through the exhaust plume of a motor vehicle as the motor vehicle passes by the system. The system also comprises one or more detectors arranged to receive the radiation after it passes through the exhaust plume of the vehicle. One or more filters may be associated with the one or more detectors to enable the detectors to determine the intensity of EM radiation having a particular wavelength or range of wavelengths. The wavelengths may be conveniently selected to correspond to wavelengths absorbed by molecular species of interest in an exhaust plume (e.g., hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2) and nitrogen oxides (NOx) such as NO and NO2. The one or more detector output voltages represent the intensity of the EM radiation measured by that detector.
These voltages are then input to a processor. The processor calculates the difference between the known intensity of the light source and the intensity detected by the detectors to determine the amount of absorption by the particular molecular species (based on predetermined wavelengths associated with that species). Based on the measured absorption(s), the concentration of one or more molecular species in the emissions may be determined in a known manner.
A system for the remote sensing of exhaust opacity is disclosed in xe2x80x9cFeasibility of Remote Sensing of Particulate Emissions From Heavy-Duty Vehicles,xe2x80x9d Chen, G. et al., American Society of Automotive Engineers (1996). In this system, opacity is measured at a wavelength of 638 nm and correlated with CO2 measurements.
Existing RES systems suffer from various drawbacks and limitations. These factors may lead to erroneous readings, a relatively high incidence of discarded data or a relatively high incidence of xe2x80x9cflaggedxe2x80x9d test results. These and other problems can reduce the benefits of an RES system.
At least some RES systems work, in part, by determining the absorption (or transmittance) of light through an exhaust plume. By determining the absorption/transmittance at particular wavelengths (corresponding to wavelengths at which various molecular species present in an exhaust plume absorb EM radiation), the concentration of those species in the exhaust can be determined. One problem is that various outside factors may affect the measured intensity and lead to errors. For example, if the measured intensity is reduced due to light scattering by particles in the exhaust plume, rather than absorption of the radiation by the species of interest, this can lead to errors.
One drawback of some remote sensing systems is the use of a single wavelength of EM radiation to measure opacity. It is known that EM radiation scattering due to the presence of particles increases with decreasing wavelength. Because scattering is a major contributor to a plume""s opacity, systems that measure opacity with only relatively long wavelength EM radiation may often yield inaccurate results.
These and other drawbacks exist.
One advantage of the invention is that it overcomes these and other drawbacks in existing devices.
Another advantage of the present invention is to provide a remote emissions sensing system and method that is capable of remotely monitoring the opacity of exhaust from vehicles.
Another advantage of the invention is to improve the accuracy of remote emissions sensing systems and methods by measuring exhaust opacity and utilizing that measured exhaust opacity to ensure the accuracy of other measurements.
Another advantage of the invention is to provide existing emission monitoring equipment with exhaust opacity monitoring capability.
These and other objects of the invention are accomplished according to various embodiments of the present invention. According to one embodiment, a RES system and method comprises a radiation source that is arranged to pass a beam of radiation through the exhaust plume of a motor vehicle as the motor vehicle passes by the system. One or more detectors are arranged to receive the radiation after it passes through the exhaust plume of the vehicle.
The one or more detectors output a voltage corresponding to the intensity of the radiation received by that detector. These voltages are then input to a processor. The processor calculates the difference between the known intensity of the light source and the intensity detected by the detectors to determine the amount of absorption by the particular molecular species (based on predetermined wavelengths associated with that species). Based on the measured absorption(s), the concentration of one or more molecular species in the emissions may be determined.
According to one aspect of the invention, the output of a reference detector is supplied to a processor and monitored by the processor to determine the opacity of each exhaust plume. Based on the measured opacity, a predetermined action may be taken. For example, if the exhaust opacity exceeds a predetermined level, the emissions data may be analyzed to produce test results (in a known manner), but the test results may be xe2x80x9cflaggedxe2x80x9d as suspect or discarded.
According to another embodiment of the invention, a system and method for measuring opacity comprises multiple sources of EM radiation having diverse wavelengths and the appropriate detector or detectors to detect the diverse wavelengths. The multiple sources of EM radiation are arranged to enable a beam (or beams) of EM radiation to pass through an exhaust emission plume. Signals from the detector (or detectors) are processed to determine, among other things, the change in intensity (e.g., intensity without emission plume present versus intensity with emission plume present) for each of the wavelengths. The change in intensity is correlated to the relative concentration of at least one emission plume constituent (e.g., carbon dioxide (CO2)). Change in intensity measurements that correlate to a sufficient degree (e.g., a regression with a standard error of the slope less than 20% of the slope value) are registered as valid opacity values.
Another embodiment of the invention enables calculation of a smoke density value that is proportional to the opacity of the plume. This embodiment may comprise a substantially monochromatic EM radiation source (e.g., a laser, or other monochromatic source) that directs EM radiation through a volume of an emission plume. Appropriate detectors obtain a measurement of the transmittance (T) of the beam through the plume. A measurement of an amount of an exhaust constituent (e.g., CO2) is performed for substantially the same volume of the emission plume. The calculation of the smoke density value for the plume is made using the measured transmittance value (T) and the measured amount of exhaust constituent.
Other objects and advantages of the present invention will be apparent to one of ordinary skill in the art upon reviewing the description herein.